JP 2013-253530 A shows a background art.
In this patent literature, a step-up converter in a fuel injector repeats ON/OFF of a current between an upper and lower limit values of a threshold so as to maintain an average current constant by switching control. Also, when the current value reaches a certain value, the average current is maintained to be constant. Stepping up from start to the above certain value is performed at one time, not in a stepwise manner. According to the above, the higher the average current value to be maintained constant is, the larger the current fluctuation at the time when stepping up is started is. Accordingly, voltage changes in signal lines around the circuit is generated by electromagnetic induction. Also, when stepping up is stopped, the larger the average current value to be maintained constant is, the larger the current drop amount is. Therefore, similarly to the above, voltage changes in the signal lines around the circuit are generated by the electromagnetic induction. Since the voltage changes in the signal lines are not intended, there is a possibility that the voltage changes cause a circuit malfunction.
Also, for example, JP 2012-159049 A shows another background art. In the present patent literature, a step-up switching element and a switching element for controlling fuel injection valve opening are concurrently turned ON in a fuel injector, and a current flown into the fuel injecting valve is increased from zero. When the current value reaches the upper limit value, the switching element of the step-up circuit is blocked. After that, the current flown into the fuel injecting valve is continuously increased by the current supplied from the switching element for controlling the fuel injection valve opening due to a rise of a power source voltage and the like. In this case, since the current exceeds the current upper limit threshold of a target current value, the current cannot be suppressed. Therefore, the current is stably retained by having a second current upper limit threshold. In the present patent literature, similarly to the above, stepping up from the start to the target current value is performed at one time. Accordingly, the larger the target current value is, the larger the current fluctuation generated at the time when stepping up is started and stopped is, and the voltage changes caused by electromagnetic induction have a large effect on the signal lines around the circuit. Since the voltage changes in the signal lines are not intended, there is a possibility that the voltage changes cause a circuit malfunction.